Overkill 3

This achievement may currently be unobtainable, as the mission (8) Gates of Hell in Suburbs crashes every time I try play it. There hasn't been even one exception, I've tried like 20 times, it always crashes.

Let me know if it does the same for you. You need around 105-110 challenge stars to unlock this mission.

Edit: it seems that a patch fixed this problem. I'll update a proper guide when I have time.